5 replies to this topic

[Gradstudent78]

I've been using a stock reagent that comes in 1 mg/mL and diluting it 1:7500 in two steps.
Adding 10 uL to 4.990 mL buffer and then 750uL into 10.5 mL buffer.

The company has changed the stock concentration to 1.25 mg/mL and I want to redo the calculation to ultimately end up at the same final concentration.

I'm not really sure how to do this or where to even start with it. Any suggestions would be welcome.

Thanks.

Grad.

[sgt4boston]

Your working solution is 133 ng/ml (approx)

Now the stock is 1250000 ng/ml.  So dilute it 1:100 to obtain 12,500 ng/ml then make a 1:93.9 dilution to arrive at 133 ng/ml.

[pito]

If you make the 1:100 dilution, make sure to work in volumes big enough.. making a 1:100 dilution doesnt give you a lot of room for errors..
So dont use 1µl+99µl..

And why do you need to do it in 2 steps?

[sgt4boston]

I think she wants to do it in two steps because if she wants 10 ml of 133 ng/ml and her stock is now 1250000 ng/ml, doing it in one step would be adding 1.064 ul to 10ml.  And, as you said don’t add 1 ul !

[perneseblue]

There are many ways to skin a cat. In this dilution scheme, I'll change as few things as possible to keep it familiar.

You are currently adding 10ul of 1mg/ml of OLD stock solution.
New stock solution is 1.25mg/ml

How much new stock solution does one need to add
M1V1 = M2V2
10ul * 1mg/ML = 1.25mg/ml * X volume
X  volume  = (10ul * 1mg/ML) /  1.25mg/ml  = 8ul

So
Add 8ul of 1.25mg/mL to 4.992 mL buffer and then 750uL into 10.5 mL buffer.

[Gradstudent78]

sgt4boston, on 10 February 2011 - 04:17 AM, said:

I think she wants to do it in two steps because if she wants 10 ml of 133 ng/ml and her stock is now 1250000 ng/ml, doing it in one step would be adding 1.064 ul to 10ml.  And, as you said don’t add 1 ul !

Correct, That is why I'm doing it two steps.



Thanks everyone, I'm going to go with Perneseblue's suggestion.